3.3v logic level mosfets

C

colin

Jan 1, 1970
0
Hi,
Im needing a 200v/1A nch mosfet wich can be driven from 3.3v logic,
preferably dual in s08 package but having trouble finding any, is this
asking too much ? as id rather avoid a driver if i can. ive found a few
small ones (200vds vgsth <3v) and a few much larger ones but nothing in
between.

at the moment ive got a device with pullups to 5v, (it was in my parts bin)
but this still doesnt quite cut it and it turns on at power up wich is
unwanted.

I also have lower voltage fets such as 2n7000p wich work fine driven
directly.

Colin =^.^=

M

Mook Johnson

Jan 1, 1970
0
Do you need mosfets or would a darlington due. With a beta around 5000 it
would only take 200uA to drive a 1A load.

M

maxfoo

Jan 1, 1970
0
Hi,
Im needing a 200v/1A nch mosfet wich can be driven from 3.3v logic,
preferably dual in s08 package but having trouble finding any, is this
asking too much ? as id rather avoid a driver if i can. ive found a few
small ones (200vds vgsth <3v) and a few much larger ones but nothing in
between.

at the moment ive got a device with pullups to 5v, (it was in my parts bin)
but this still doesnt quite cut it and it turns on at power up wich is
unwanted.

I also have lower voltage fets such as 2n7000p wich work fine driven
directly.

Colin =^.^=

What's wrong with the 2n7000,too big? Use a smaller BSS138 in a sot-23 package.

C

colin

Jan 1, 1970
0
maxfoo said:
What's wrong with the 2n7000,too big? Use a smaller BSS138 in a sot-23
package.

2n7000 is fine but Its only 60v rated, I need about 200v, ... 150v + some
inductive overshoot.
darlington is an idea wich I'd not thought of,
but its for a low power inverter running from the 5v so low fwd drop is
preferable.
the somewhat complex pwm control is done from a PIC. the 2n7000 is for -20v
inverter.

I think i might have to go for a driver and some beefier mosfets as I cant
get enough power from the ones I have even with 5v pullups, its not quite as
low power as id hoped lol. Il have to bring in 12 for the driver I can run
the inverter off 12v instead of 5 too.

However I did have a look at fairchild's site and its very nice to use,
found one that I might try anyway, thats if I can get hold of it - Fqt4n20.
although looking for that one in Farnell i came across a bsp297or zvn2120G
but the later is no longer stocked, They didnt stand out in previous
searches.

thanks,
Colin =^.^=

A

Anthony Fremont

Jan 1, 1970
0
Mook said:

Needs way more than 3.3V drive unless you want to cook it. Vgs(th) is 3V
max, they spec it at 10Vgs to really turn it on, 5V will turn it on some but
3.3V and it's really gonna be a bar-b-q with any current.

I'm thinking maybe the OP should look into IGBTs. I don't know about the
3.3V drive, but it's way easy to find IGBTs that will withstand 600Vds and
switch large currents. The down side is that giant cap sitting on the
gate(base). As long as you can dump the juice in fast enough, they're
slick. Of course I only played with them once and I used 5V drive. Mr Hill

C

colin

Jan 1, 1970
0
Anthony Fremont said:
Needs way more than 3.3V drive unless you want to cook it. Vgs(th) is 3V
max, they spec it at 10Vgs to really turn it on, 5V will turn it on some
but 3.3V and it's really gonna be a bar-b-q with any current.

I'm thinking maybe the OP should look into IGBTs. I don't know about the
3.3V drive, but it's way easy to find IGBTs that will withstand 600Vds and
switch large currents. The down side is that giant cap sitting on the
gate(base). As long as you can dump the juice in fast enough, they're
slick. Of course I only played with them once and I used 5V drive. Mr

That vn2224 looks realy cool, maybe I can add an offset to the gate drive of
1volts,
that will give me 4.3 volts drive and still be sure its off,
maybe set the vdd to the max of 3.6 volts and/or go for 1.2 volts, gate
offset.
the open drain 5v pull up isnt so nice when programming the device and the
outputs go tri state.

the graph shows at 1 amp its saturated at vgs=3v., I hadnt intended to need
more than 1amp,
its an inverter so the current is ramped from 0-1amp, average 50% duty
cycle, so 0.25A avg
I only need about 1.5W real power output from the device im driving,
although it seems I need a fair bit more due to reactive currents in the
at 4vgs its over 4amps wich should be ample for my needs, typical ofc.

Theres a quad package too, maybe 2 in parallell will easily do, or I can use
the other 2 to save a discrete elsewhere.

As for devices with large input capacitance such as igbt, the current from
my PIC is somewhat limited, so switching speed will become unaceptable so I
would need a driver anyway wich then makes the fet selection easy anyway.
the output from the inverter is 1/2 sine wich is why its PWM is driven from
the PIC. it should drive the 2nc gate charge of the vn2222 quick enough.

Id rather drive everything from the 5v but its a bit of a jump from 5v to
150pk and demands a bigger device but the 12v supply is via a linear
regulator, the 5v via a switcher.

Unfortunatly the VN2222 that is stocked by RS and farnell seem to be 60v
spec to92 devices.
seems to be some confusion with part numbers here >.<
is the 200v version an unobtanium part ?

Think I might just plop for a driver and be done with it. I just tried a
dual driver I had available but cldnt get it to work, then reading the data
sheet realised the shutdown input had a threshold of 11v lol.

thanks
Colin =^.^=

A

Anthony Fremont

Jan 1, 1970
0
colin said:
That vn2224 looks realy cool, maybe I can add an offset to the gate
drive of 1volts,
that will give me 4.3 volts drive and still be sure its off,
maybe set the vdd to the max of 3.6 volts and/or go for 1.2 volts,
gate offset.
the open drain 5v pull up isnt so nice when programming the device
and the outputs go tri state.

the graph shows at 1 amp its saturated at vgs=3v., I hadnt intended
to need more than 1amp,

If I understand what I'm reading, Vds will be 1V at 3Vgs and 1A, that's a
dissipation of 1W. It's gonna get real hot if you draw an amp thru it.
its an inverter so the current is ramped from 0-1amp, average 50% duty
cycle, so 0.25A avg
I only need about 1.5W real power output from the device im driving,
although it seems I need a fair bit more due to reactive currents in
at 4vgs its over 4amps wich should be ample for my needs, typical ofc.

Am I not reading this right? At Vgs=4V and Id = 4A, I come up with a Vds of
5V. Isn't that 20W of dissipation?
Theres a quad package too, maybe 2 in parallell will easily do, or I
can use the other 2 to save a discrete elsewhere.

As for devices with large input capacitance such as igbt, the current
from my PIC is somewhat limited, so switching speed will become
unaceptable so I would need a driver anyway wich then makes the fet
selection easy anyway. the output from the inverter is 1/2 sine wich
is why its PWM is driven from the PIC. it should drive the 2nc gate
charge of the vn2222 quick enough.

I agree that the PIC should have no trouble charging the gate of that
device.
Id rather drive everything from the 5v but its a bit of a jump from
5v to 150pk and demands a bigger device but the 12v supply is via a
linear regulator, the 5v via a switcher.

Unfortunatly the VN2222 that is stocked by RS and farnell seem to be
60v spec to92 devices.
seems to be some confusion with part numbers here >.<
is the 200v version an unobtanium part ?

All I know is that I couldn't find any FET that I could afford/use at 400V,
I had to use an IGBT and a gate driver:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010666
Think I might just plop for a driver and be done with it. I just
tried a dual driver I had available but cldnt get it to work, then
reading the data sheet realised the shutdown input had a threshold of
11v lol.

TC4423 by microchip $2 in singles at Digikey. Good to 18V on the output and should work fine at 3.3V. 4423 dual inverting 4424 dual non-inverting 4425 dual one-of-each C colin Jan 1, 1970 0 Anthony Fremont said: If I understand what I'm reading, Vds will be 1V at 3Vgs and 1A, that's a dissipation of 1W. It's gonna get real hot if you draw an amp thru it. Am I not reading this right? At Vgs=4V and Id = 4A, I come up with a Vds of 5V. Isn't that 20W of dissipation? yea those dissipations are quite high, its a current ramp though so only the tail end power will be that high, the average will work out a lot lower. the on resistance would of course severly limit operation to less than 4amp as id rather use 5v for the inverter. At 12v i would need less current too ofc. I agree that the PIC should have no trouble charging the gate of that device. Well depends how fast you want to switch it, 100khz would be ideal. the dspic33 is a bit weedy on the io pin current side. rated 4ma but seems to easily sink a peak of 10ma. All I know is that I couldn't find any FET that I could afford/use at 400V, I had to use an IGBT and a gate driver: http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010666 I had a dual SO8 500v mosfet wich i used as a class d stage, fed by an inverter. Im trying to simplify it drastically by doing away with the inverter and the hi and low side driver. TC4423 by microchip$2 in singles at Digikey. Good to 18V on the output
and should work fine at 3.3V.
4423 dual inverting
4424 dual non-inverting
4425 dual one-of-each

dual low side drivers should be cheaper than that I hope,
I dont need 3amp gate drive, thats as much as drain current,
or discrete will do.

thanks
Colin =^.^=

L

[email protected]

Jan 1, 1970
0
Hi,
Im needing a 200v/1A nch mosfet wich can be driven from 3.3v logic,
preferably dual in s08 package but having trouble finding any, is this
asking too much ? as id rather avoid a driver if i can. ive found a few
small ones (200vds vgsth <3v) and a few much larger ones but nothing in
between.

at the moment ive got a device with pullups to 5v, (it was in my parts bin)
but this still doesnt quite cut it and it turns on at power up wich is
unwanted.

Does pullup to 5V really help any? won't the voltage just get clamped
by the output to something close to 3.3V?

-Lasse

A

Anthony Fremont

Jan 1, 1970
0
colin said:
yea those dissipations are quite high, its a current ramp though so
only the tail end power will be that high, the average will work out
a lot lower. the on resistance would of course severly limit
operation to less than 4amp as id rather use 5v for the inverter. At
12v i would need less current too ofc.

Well depends how fast you want to switch it, 100khz would be ideal.
the dspic33 is a bit weedy on the io pin current side.
rated 4ma but seems to easily sink a peak of 10ma.

Ok, most of the ones I tinker with will supply 20mA.
I had a dual SO8 500v mosfet wich i used as a class d stage, fed by an
inverter.
Im trying to simplify it drastically by doing away with the inverter
and the hi and low side driver.

dual low side drivers should be cheaper than that I hope,
I dont need 3amp gate drive, thats as much as drain current,
or discrete will do.

Those are for fairly healthy sized MOSFETs and IGBTs. Microchip's AN786 app
note might interest you. It has some good info on how to "correctly"
calculate the amount of drive current you will really need to switch in a
certain amount of time. Those microchip gate drivers above will switch in
30nS or better. I guess it all depends upon what you need.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011878
It's about PWM'ng power supplies that have high and low side drive, but
might interest you anyway.

C

colin

Jan 1, 1970
0
Does pullup to 5V really help any? won't the voltage just get clamped
by the output to something close to 3.3V?

the particular PIC outputs can be set to open drain and then have a 5v
tolerance.

Colin =^.^=

W

whit3rd

Jan 1, 1970
0
Im needing a 200v/1A nch mosfet wich can be driven from 3.3v logic,
I also have lower voltage fets such as 2n7000p wich work fine driven
directly.

If your present mosfet drives OK, and you really care about high
voltage,
consider a cascode. Either another MOSFET, or (I'd prefer this)
an NPN transistor, with base connected to your 3.3V rail, should fit
the
bill. Connect the base through a parallel RC to get lower ON
voltage.

It's not a perfect switch-to-ground, but it's quite easy to drive.

C

colin

Jan 1, 1970
0
whit3rd said:
If your present mosfet drives OK, and you really care about high
voltage,
consider a cascode. Either another MOSFET, or (I'd prefer this)
an NPN transistor, with base connected to your 3.3V rail, should fit
the
bill. Connect the base through a parallel RC to get lower ON
voltage.

It's not a perfect switch-to-ground, but it's quite easy to drive.

yes a cascode arangment that was something I had considered as an
alternative to a driver.
and a 2 mosfet cascode needs no extra resistors.

Colin =^.^=

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